Here's a question: why is there no trapping (as in the majority of aikido waza) in MMA? Or perhaps I should ask, has anyone managed to pull off locks against a good, resisting opponent?

Is aikido just made up of low-percentage techniques? Or are there just not enough skilled aikido people trying MMA?

I think there are a couple of different ways of looking at it.

In one sense, MMAists use Aikido locks all the time. Or to be more precise, MMAists and Aikidoists use the same locks differently. There are only so many positions for locking an arm; the Filipinos identify them as branch out, branch up, and branch down. There are only so many ways to lock the wrist, too. By definition, any system using joint locks uses these reference points, and doesn't matter whether it's standing or on the ground. BJJ's juji garame and Aikido's elbow lock are the same thing because they're both branch out, even though the former is executed on the back and the latter is done standing.

In another sense, one issue is that freestyle training has to be consistent with what an art does inorder to try it techniques in those areas. Most Aikido techniques, when you're doing them, involve nage starting out at almost boxing range but then getting very close to uke, sometimes body-to-body, for all or part of the technique, and "traditionally" stops short of ground fighting. So it is not kickboxing and not ground grappling but nestled somewhere in between; most MMA people probably blast through that range during a takedown. Furthermore, 99% of the time, Aikidoists go for a joint lock right off the bat (shiho nage included; it's really a branch up shoulder lock); doing that sort of thing freestyle is a question of safety so musles and ligaments don't get torn.

Can aikido-style locks be applied kick-boxing? Probably, but it has to be touch-and-go, automatic, without time to think about it! I was sparring with my jun fan sifu some weeks ago, and at one point he through a jab; when I felt the crotch of his elbow go under my lead arm, I autmatically brought both arms down and plastered his forearm to my chest. I wasn't sure how to go for a lock from there (although he liked it), but the point is that was an automatic reaction; if I had tought, "Oh, I'll try this trap," it would have been too late.

So I look on the repitition of Aikido techniques as the meat and potatoes of the training; I see it as repetitive drilling meant to hardwire those reference points into you so you instantly recognize them. It may not be a good way to get intellectual understanding, but that's not what they want -- they want to ingraine something. How that comes out kickboxing or grappling, I don't know for sure, but that's what you can look for in that training. It's also why I think once a week is minimum for Aikido training if you're looking to get anything out of it; otherwise you won't retain enough.